1. Field of the Invention
The present invention relates to an image forming apparatus implemented by a distributed control system including a plurality of CPU groups having a hierarchical structure.
2. Description of the Related Art
Centralized control using one CPU is performed for printer device control of an image forming apparatus using an electrophotographic system. With an increase in CPU load due to control centered on one CPU, a higher performance CPU is required. In addition, with an increase in printer device load, it is necessary to lay in communication cables (a bundle of communication lines) from a CPU board to distant load driver units. This requires many long communication cables. In order to solve this problem, much attention has been paid to a control form of assigning the respective control modules constituting an electrophotographic system to sub-CPUs.
Examples of constructing control systems by distributing the respective partial module control functions using a plurality of CPUs have been proposed in several control equipment product fields other than copying machines. For example, Japanese Patent Laid-Open No. 2000-071819 has proposed a technique of hierarchically locating functional modules in a vehicle and performing distributed control. Japanese Patent Laid-Open No. 2006-171960 has proposed a technique of applying a similar hierarchical control structure to robot/automation equipment. These sub-CPUs require a communication unit to make them operate as a system as a whole. Japanese Patent Laid-Open No. 2006-171960 has proposed a technique of constructing different communication networks for the respective hierarchical layers for a control network for performing communication among functional modules, thereby constructing a stable control network by load distribution.
However, the above prior arts have the following problems. For example, in a vehicle or the like, based on the premise that a plurality of control modules which are physically distant from each other implement large-capacity data communication and ganged control requiring fast responsiveness, the respective modules are connected to each other via a large-sized, high-speed network. Large-capacity data communication in this case is, for example, communication between a car navigation system and an instrument panel control system. In addition, ganged control is, for example, anti-lock brake control implemented by ganging a steering angle (steering wheel) control module with a brake control module.
When such a system arrangement is directly applied to distributed control of an image forming apparatus, since control of each unit of the image forming apparatus requires precise timing control, the respective modules at higher hierarchical layers are connected to each other via a high-speed network. Since a high-speed network communication unit itself is expensive, the cost of the apparatus increases. As described above, when divisional control is to be applied to an image forming apparatus, an increase in cost due to connection via a high-speed network poses a problem.